This invention relates in general to weight-displaying devices and in particular to electronic weight-measuring devices.
Weight-measuring and displaying devices are available in a variety of types and sizes depending upon the particular application and the weight range to be encountered. In order to assure full indicator scale accuracy, most weight measuring devices are designed for particular uses and the internal construction of such devices corresponds with the intended application. For example, a scale designed to weigh metal bar stock in units of tons is not suitable as a scale to detect differences of only a few pounds. One type of scale which is capable of detecting weight variations of a few pounds are bathroom scales. Such scales are typically designed with a full dial range of up to 300 pounds, and are able to reflect weight differences of approximately one to two pounds. However, such scales have a variety of disadvantages such as, for example, the need to frequently be re-zeroed because variations may occur between the time one reading it taken and the next time the scale is used. Further disadvantages with such scales are the inability to read the dial indicator accurately and the fact that such scales are often heavy and bulky.
With the introduction of solid state electronic technology, it is possible to convert conventional dial indicator readings into digitally displayed numerical values that are accurate and repeatable (when the actual weight is the same). The following list of patents provides some indication of the types of electronic scale concepts which have been devised:
______________________________________ Patent No. Patentee Issue Date ______________________________________ 3,655,003 Yamajima 4/11/72 3,838,744 Tanji et al. 10/01/74 3,770,069 Loshbough 11/06/73 3,967,690 Northcutt 7/06/76 ______________________________________
Yamajima discloses a weighing machine which includes an adjustable height scale ring in concentric relation with the weight scale dial so that a person being weighed may recognize at a glance his actual weight relative to the optimum weight for a particular height. This device does not actually provide any new design to the basic scale mechanism, it only adapts a new feature to such a conventional scale.
Tanji et al. discloses an electronic weight-measuring device wherein the user's weight is displayed by digital display tubes and this weight may be displayed in a plurality of locations remote from the platform of the scale on which the user stands. The disclosure of this patent deals primarily with the manner in which a plurality of remote display devices can be used and there is virtually no mention of the electronics which are employed for such display devices. It is not clear whether such a device overcomes the problems with accuracy and repeatability of conventional scales, but it is apparent that the design disclosed has not attempted to solve the weight and bulkiness problems associated with conventional bathroom scales.
Loshbough discloses a control circuit for an electronic computing scale which computes the value of an article based upon a predetermined price per unit weight for the article. The requirement of being a computing scale creates an added expense to the scale due to the extent of the electronics involved, and such a device is too complex to serve as a conventional bathroom scale.
Northcutt discloses an electronic digital readout diet scale which includes electronic circuitry for accurately detecting and displaying minute changes of weight in a dieter. A voltage-controlled oscillator puts out a frequency (dependent upon voltage input) in the form of a number of cycles per unit of time. One problem with voltage-controlled oscillators is that the time base must be very accurate and in order to achieve this accuracy, the time should be crystal controlled. However, the use of crystal control for a device such as a scale is not desirable because of the fact that crystals are not able to withstand even moderate levels of mechanical vibrations. A further shortcoming with the Northcutt device is that the voltage-controlled oscillator and the time base oscillator are not in phase and an error of plus or minus one cycle could result. Although such an error could be rounded off, it is still a disadvantage to have such error present with the device.